Intermittent fasting: another nutrition fad?

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by Rod Navajas

Atkins, Paleo, Juice Cleanse, Weight Watchers, Carnivore, Ketogenic…the list goes on. If you have not yet heard any of these different terms, you are either living under a nutrition rock or have no interest in health, fitness and nutrition. 

What do all these different diets have in common? They all promise to reduce your waistline and be the ultimate solution for your fight with the scales once and for all. Do they work? Sure. In the long run? Maybe, but unlikely. For everyone? Definitely not. 

More recently, another diet term frequently used and thrown around is intermittent fasting. Highly popularized by the 5:2 diet which was introduced by Michael Mosley, intermittent fasting is one of the latest nutrition trends of the century. The question is: is intermittent fasting the fat loss solution everyone has been looking for? 

What is Intermittent Fasting? 

Intermittent fasting is a broad term that means cycling between periods of restricting calories and periods of not restricting calories. While fasting, you may either avoid all foods and beverages with calories or greatly limit your calorie intake. There are several different types of Intermittent Fasting, the most popular are listed below:

  1. Time-restricted eating means you only eat during a set window of time, which may range anywhere from 4 to 12 hours. For example, you might only eat between 8 a.m. to 4 p.m. This means 16 hours of fasting and an 8-hour eating window. 
  2. Alternate-day fasting (ADF), also called fasting intervals, means a cycle of fasting on one day and then normal food intake the next day. You only consume water and electrolytes on fasting days. 
  3. Intermittent energy restriction (IER) or modified fasting means switching between days of eating a very low-calorie diet and normal calorie intake. The days you restrict calories may either be in a row or split up during the week. Two examples of this type of fasting are: 
    • Modified alternate-day fasting. This is like alternate-day fasting, except you can eat up to 600 calories or 25% of your daily calorie needs on the days you fast. For example, if you need 2,000 calories daily to maintain your weight, you’d only eat 500 calories (25% of your needs) on days of fasting. 
    •  5:2 method. This means that on two days of the week, you have a very low-calorie intake (no more than 25% of your daily calorie needs). On the other five days, you have a normal calorie intake. 
The 5:2 diet - 2 days of restricted caloric intake and 5 days of normal eating
Fig 1. The 5:2 diet – 2 days of low caloric intake and 5 days of normal caloric intake over 7 days

Is intermittent fasting better for weight loss?

One fundamental aspect when comparing different dietary approaches for weight loss, is to ensure that calories are equated for – meaning that both approaches deliver the same amount of calories to participants over the same period.

When we look at studies comparing intermittent fasting to continuous caloric restriction (including reviews and meta-analysis), we can see that when calories are matched, intermittent fasting is not superior for weight loss to continues caloric restriction (1, 2, 3). Once again, what really seems to matter for weight loss, beyond any other aspect, is the amount of calories consumed over a period of time. 

Benefits beyond weight loss

When we speak about calories, we are focusing on one nutritional aspect only: ‘The quantitative factor’. This takes into consideration the quantity of protein, fat and carbohydrate, and consequently the calories, one consumes. But the types of foods you consume, the way they are processed and when you consume them have different effects in the body. This is what I call ‘The qualitative factor’. Intermittent fasting has been shown to elicit positive effects in the body beyond weight management. 

The activation of the Migrating motor complex (MMC) is one of the most underrated benefits of intermittent fasting. MMC is known as a “cleanse wave” of the digestive system and its activation, which happens during fasting and is interrupted by feeding, has been associated with lower rates of Small Intestine Bacteria Overgrowth or SIBO, which is responsible for some of the most common digestive symptoms such as bloating and abdominal pain (4). 

Important cardiometabolic improvements occur with intermittent fasting in the absence of weight loss. Insulin sensitivity, blood pressure and oxidative stress levels have all been shown to improve with time-restricted eating even when calories are matched (5). In fact, blood sugar regulation seems to be one of the positive effects of intermittent fasting without any caloric restriction (6). 

Who should avoid Intermittent Fasting?

No dietary approach is suitable for every individual. Intermittent fasting is no exception.

Children, frail adults, underweight, pregnant or trying to become pregnant, or breastfeeding should not fast. Individuals with an eating disorder or disordered eating pattern and individuals with adrenal fatigue should also steer clear of intermittent fasting (7).

The missing component…

Although intermittent fasting seems to produce additional benefits beyond weight loss, it is not superior to continuous caloric restriction when it comes down to body composition outcomes.  

The forgotten factor in all those different dietary approaches is individuality. Everyone will require a unique diet template based on current presentation, food preferences and intolerances, nutrient deficiencies and feasibility.

To put simply, a perfect plan will not be perfect for everyone. A nutritionist can help you navigate through all those different approaches and select what is best for you. 

Remember that when reading about the latest diet fad! 

References:

  1. Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss. Nutrients11(10), 2442.
  2. Kim, K. K., Kang, J. H., & Kim, E. M. (2022). Updated Meta-Analysis of Studies from 2011 to 2021 Comparing the Effectiveness of Intermittent Energy Restriction and Continuous Energy Restriction. Journal of obesity & metabolic syndrome31(3), 230-244.
  3. Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., … & Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and cellular endocrinology418, 153-172.
  4. Deloose, E., Janssen, P., Depoortere, I., & Tack, J. (2012). The migrating motor complex: control mechanisms and its role in health and disease. Nature reviews Gastroenterology & hepatology9(5), 271-285.
  5. Harvie, M. N., Pegington, M., Mattson, M. P., Frystyk, J., Dillon, B., Evans, G., … & Howell, A. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International journal of obesity35(5), 714-727.
  6. Bitsanis, D., Giannakou, K., Hadjimbei, E., & Chrysostomou, S. (2022). The Effect of Early Time-Restricted Feeding on Glycemic Profile in Adults: A Systematic Review of Interventional Studies. Review of Diabetic Studies18(1), 10-19.
  7. Nakamura, Y., Walker, B. R., & Ikuta, T. (2016). Systematic review and meta-analysis reveals acutely elevated plasma cortisol following fasting but not less severe calorie restriction. Stress19(2), 151-157.

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